In a recording head to be mounted in an ink jet recording apparatus, a representative ink discharge method is a method utilizing an electrothermal converting element. In this method, an electrothermal converting element is provided in a liquid chamber and is given an electrical pulse as a recording signal to supply a recording liquid with thermal energy, and a pressure of a bubble generated in the recording liquid by a phase change therein is utilized for discharging a droplet of the recording liquid. Such ink jet recording head includes a liquid discharge substrate which discharges a droplet of a recording liquid and an ink supply system for supplying the liquid discharge substrate with the ink.
The liquid discharge substrate is provided with a device substrate having electrothermal converting elements and liquid discharge ports in plural pairs, and a flow path forming member which is laminated on the device substrate to define a space enclosing each electrothermal converting element, and a discharge port for the recording liquid droplet and an ink supply path, communicating with each space. The liquid discharge substrate is supported by a support member having a liquid supply opening, and electrode lead terminals of an electric wiring board, which supplies the liquid discharge substrate with an electrical drive signal and a driving power, are electrically connected with electrodes formed on a surface of the liquid discharge substrate, at the side of the discharge ports.
Recently the ink jet recording apparatuses are experiencing a significant price erosion, so that the manufacture of the ink jet recording head as inexpensively as possible is becoming a major issue. For this purpose, a dimensional reduction of the liquid discharge substrate is particularly effective. A smaller size of the liquid discharge substrate allows to obtain a larger number thereof from a single wafer, thus enabling a cost reduction of the recording head.
However, a dimensional reduction in the liquid discharge substrate of the above-described structure results in following drawbacks.
With the liquid discharge substrate made smaller in size, an adjoining area of the liquid discharge substrate to the support member becomes smaller while the number of the electrothermal converting elements remains unchanged, so that the heat generated by the electrothermal converting elements in the driven state tends to be accumulated in the device substrate. As a result, the discharge control utilizing the bubble generation in the liquid may be detrimentally affected. Therefore, in order to dissipate such heat efficiently from the liquid discharge substrate, the supporting member has to be given a high heat dissipating property.
Also with the liquid discharge substrate made smaller in dimension, the connecting parts of the electrode terminals for supplying the electric power and the drive signal become smaller in size and pitch, whereby the connectivity becomes difficult to secure. It therefore becomes difficult to form, as in the liquid discharge substrate of prior art, the electrodes to be connected with the electrode terminals for supplying the electric power and the drive signal, on the surface of the substrate.
As a prior recording head capable of solving the issue of connectivity, patent reference 1 discloses a printing head bearing electrical connecting electrodes on a surface opposite to the surface bearing the discharge ports.
FIG. 26 is a partial cross-sectional view, including a printing head die and a supporting substrate and showing the structure for electrical connection in an ink jet printing head disclosed in Japanese Patent Application Laid-open No. 11-192705.
Referring to FIG. 26, a print head 218 is mounted on a supporting substrate 220. The print head 218 has electrodes 284 for electrical connection and an ink supply opening 242 on a surface opposite to the surface including a discharge nozzle aperture 238. The supporting substrate 220 for supporting the print head 218 is provided with electrical wirings on a first surface 270 and on a second surface 272. The print head 218 is electrically connected and supported, by solder bumps, on the first surface 270 of the supporting substrate 220. A logic circuit (not shown) and a drive circuit 230 are provided on the second surface 272, opposite to the first surface 270 of the supporting substrate 220.
Also as a prior example of the supporting substrate for supporting the liquid discharge substrates, Japanese Patent Application Laid-open No. 2002-86742 discloses a carrier for a purpose of precisely aligning plural liquid discharge substrates. The carrier includes a substrate formed by plural layers, and a mounting layer laminated on the substrate and serving to mount the liquid discharge substrate, and the purpose is attained by planarizing a surface of the mounting layer, opposite to the substrate. The mounting layer constituting such supporting substrate, called a carrier, is provided with an opening, which communicates with the ink supply opening of the liquid discharge substrate mounted on the mounting layer. Also the substrate bearing the mounting layer is provided with an opening penetrating through the layers constituting the substrate, and such opening communicates, as an ink flow path, with the opening of the mounting layer. Also in order to supply the liquid discharge substrate with an electrical signal, the carrier is provided with an electrically conductive path penetrating through the layers of the substrate, from the rear surface to the top surface of the carrier. The carrier is provided, on the surface thereof, with an electrode pad constituting a terminal part of the conductive path. Such electrode pad is electrically connected, by a bonding wire, with an electrode formed on a surface, including the discharge port, of the liquid discharge substrate.
However, the structure of the print head (liquid discharge substrate) and the supporting substrate, disclosed in Japanese Patent Application Laid-open No. 11-192705, involves following drawbacks.
The supporting substrate for supporting the liquid discharge substrate, being formed by a one-layered substrate, has a limited heat capacity and is unable to efficiently absorb the heat, generated when the electrothermal converting element on the liquid discharge substrate is activated, by the supporting substrate, thus being poor in the heat dissipating property.
Also in case of forming solder bumps on the electrodes on the rear surface of the liquid discharge substrate as shown in FIG. 26 and connecting the liquid discharge substrate on the supporting substrate under a predetermined load on such bumps, there may result a deformation of the supporting substrate or a defective connection of the electrode terminal. More specifically, as shown in FIG. 26, the print head has the ink supply opening 242 on a surface thereof opposed to the supporting substrate 220, and solder bumps are formed on rear electrodes 284 formed on a rim portion of the ink supply opening 242. On the other hand, the supporting substrate 242 is provided with an opening communicating with the ink supply opening 242 of the print head, and electrodes are formed on the rim portion of such opening for connection with the solder bumps. The supporting substrate 220 is not supported under the rim portion of the opening, to be connected with the solder bumps, and may therefore be deformed at the connection with the solder bumps, thereby deteriorating the connectivity of the solder bumps.
Particularly in case of forming a penetrating electrode from the top surface to the rear surface of the supporting substrate, such supporting substrate is usually prepared thinner, as a long penetrating electrode requires an elevated production cost. For this reason, in case the supporting substrate is not supported under a portion to be connected with the solder bump as disclosed in Japanese Patent Application Laid-open No. H11-192705, it shows a deficient strength in supporting and connecting the liquid discharge substrate, resulting in a deformation of the supporting member or a connection failure in the electrode terminals.
Also in the recording head structure shown in Japanese Patent Application Laid-open No. 2002-86742, electrodes on a surface, including the discharge port, of the liquid discharge substrate and electrode pads of the supporting substrate on the surface thereof mounting the liquid discharge substrate are connected electrically by bonding wires. Therefore, when the pitch of the electrodes is made smaller by a dimensional reduction in the liquid discharge substrate, connection with such bonding wires becomes difficult to achieve. Also Japanese Patent Application Laid-open No. 2002-86742 does not cover the aspect of improving the heat dissipating property in the structure of the supporting substrate.